Teaching organic synthesis at post-16

We use many different synthetic molecules in our everyday lives. These are found in obvious products like medicines, but also in our food, detergents and clothing. A glance at the ingredients list of any of these products reveals a huge variety of compounds. All these molecules are made in chemical plants and their synthesis generally requires more than one step. Chemists carefully design their synthetic routes to balance the yield and purity of product with other factors like the rate of reaction, hazards and waste implications.

Organic synthesis is based on the versatility of carbon atoms. Carbon can form four bonds per atom; it can form single, double or triple bonds, and can bond with many elements – and with itself. The synthetic pathways that can be drawn for organic molecules are infinite, although thankfully not within the confines set by most advanced chemistry specifications.

What students need to know

The exact range of synthetic routes covered differs by exam board, so check exactly which ones are required for your class. This topic is the very last part of organic chemistry for most courses, where all the individual parts form a bigger picture. This means that students need a lot of varied knowledge to access questions and successfully answer them.

Typically, students need to able to:

• state reagents and conditions for the interconversion of functional groups in individual or multiple steps in a synthesis.
• confidently switch between the multiple representations of compounds, such as empirical, molecular, displayed and skeletal formula, as well as be able to apply meaning to those structures.
• name and outline the mechanism for particular transformations.
• identify the structure of missing reactants, products and by-products in reaction schemes.
• give reasons for the structural or stereoisomerism observed in schemes.

Common misconceptions

It’s common for students (and teachers) to think of synthesis as a vast body of facts that needs to be learned. Although this is the case for some aspects, like reagents and conditions, these simple recall items don’t tend to make up many of the marks for the topic in exams. Students will meet with relatively limited success if they just try to learn facts, no matter how much retrieval practice they do.

Students may also struggle to consider alternative reactants or ways to solve problems if they have just learned each reaction as an isolated fact. For example, if a student learns that a particular reaction uses sodium hydroxide, they may not recognise that the reaction with potassium hydroxide is likely to proceed in a similar fashion.

Ideas for your classroom

Checking students’ understanding

Individual strands within organic synthesis lend themselves to quick retrieval of some aspects and, because students often leave practice to the last minute, regular quick formative quizzes are helpful to build knowledge over time. You can use a number of different quiz techniques to add variety; quiz apps can be motivating for students.

Gap filling exercises, where students are given partial schemes and asked to add structures, are an effective way to practise problem solving. Make sure you include different representations of molecules in any questions so students can gain confidence with multiple representations.